Not Applicable.
Not Applicable.
(1) Field of the Invention
This invention relates to an on-line process for removing copper deposits from the blades of the rotor of a steam turbine in systems, particularly condensing steam turbines. The process comprises adding an oxime to an appropriate injection point of an electric generating power plant powered by a steam turbine, where the power plant comprises a pre-boiler system, a steam generator, a steam turbine, a condenser and an electric generator.
(2) Description of the Related Art
Steam turbines are an important power source used to generate electricity. The steam turbine is part of an electric power plant that contains, among other equipment, a pre-boiler system, a steam generator, a steam turbine, a condenser, and an electric generator.
Typically, the source of the steam for the steam generator is a natural geothermal source or an artificial source generated by superheating a reservoir of water and directing it to the steam turbine. The source of heat for superheating the water is typically a fossil fuel or a nuclear reactor.
Among other components, steam turbines contain blades attached to a rotor. The force of the steam on the blades causes the rotor to rotate and drive an electric generator. Typically, many components of the steam generator and steam turbine (e.g. heat exchangers, condensers, pipes, valves, pumps, etc.) are made of an alloy of copper and nickel, mostly copper.
In addition, during the assembly of the steam system components, it is sometimes necessary to utilize materials (anti-seize compounds) designed to reduce the work required for assembly and the future disassembly of the components. High-temperature anti-seize compounds may contain copper-bearing components.
Because these components are exposed to high temperatures and pressures, and severe operating conditions, the copper volatilizes and deposits on the blades of the steam turbine as oxides of copper.
As these deposits build up on the turbine blades, the efficiency of the steam turbine decreases. (See xe2x80x9cUtilities contend with copper to enhance cycle reliabilityxe2x80x9d, Straus, Power Magazine, January, 1992; xe2x80x9cCopper in Fossil Plant Cyclexe2x80x9d, Dooley, EPRI, 1999; and xe2x80x9cState of Knowledge of Copper in Fossil Plant Cyclesxe2x80x9dxe2x80x94EPRI, 9/97, TR-108460.) These deposits change the surface characteristics of the metal blade and decrease the operating efficiency of the steam turbine. (See xe2x80x9cSteam Turbine Efficiency and Corrosion-Effects of Surface finish, deposits, and moisturexe2x80x9d, Jonas, et al, EPRI, Summer, 2000; xe2x80x9cCopper Deposition and MW Loss Problem Solutionsxe2x80x9d, Proceedings of the International Water Conference, 1996). The decreased in efficiency often amounts to ten to fifteen percent of the rated generator output. In order to increase the efficiency of the steam turbine, the equipment must be shut down and cleaned. (See xe2x80x9cChemical Cleaning of HP Turbinesxe2x80x9d, Columbia Energy Centerxe2x80x94Lawrence, IWC-95-68.) This decrease in efficiency results in lost revenue and increased expenditures.
It is known to use methyl ethyl ketoxime (MEKO) as an oxygen scavenger and metal passivator in boilers. See, for instance, U.S. Pat. No. 4,487,745. This patent indicates that the amount of oxime used in treating boiler water is from 0.0001 ppm to 500 ppm, although commercial utility plant experience indicates that the typical dosage of MEKO used to control feedwater oxygen scavenging is from 30-80 ppb. MEKO controls corrosion in the feedwater circuit by scavenging oxygen and by establishing a corrosion-resistant oxide film on waterside metallic surfaces.
All citations referred to under this description of the xe2x80x9cRelated Artxe2x80x9d and in the xe2x80x9cDetailed Description of the Inventionxe2x80x9d are expressly incorporated by reference.
This invention relates to an on-line process for removing copper deposits from the blades attached to the rotor of steam turbine wherein said process comprises:
adding an effective copper deposit-removing amount of an oxime to an injection point of an electric generating power plant comprising a pre-boiler system, a steam generator, a steam turbine, a condenser, and an electric generator,
such that the system contains a source of copper, and
such that the oxime reaches a temperature of at least 30xc2x0 C. and contacts the blades attached to the rotor of the steam turbine.
The source of copper usually is from one or more components comprised of alloys containing copper and/or additives comprised of a copper and/or or anti-seize additives. The injection of the oxime is effective in reducing or removing the copper deposits from the turbine blades. Consequently, the steam turbine operates more efficiently, and shut downs are reduced or eliminated.
Not Applicable.
The detailed description and examples will illustrate specific embodiments of the invention will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed. All units are in the metric system and all percentages are percentages by weight unless otherwise specified.
An electric power plant powered by a steam turbine typically comprises (1) a pre-boiler/feedwater facility, (2) a steam generator, (2) a steam turbine, (3) an electric generator, (4) valves, (5) pumps, and (6) possibly a condenser, evaporator, and/or deaerator, as well as other components.
A pre-boiler system can be composed of one or more low pressure feedwater heaters, a deaerating heater, boiler feed pumps, one or more high pressure feedwater heaters, and an economizer. All pre-boiler system components except for the boiler feed pumps are designed to heat the water prior to the boiler. This reduces the amount of fuel required to convert the water to steam in the steam generator.
The steam generator is the source of steam. The source of the steam may be natural occurring geothermal steam, or steam produced by superheating water by means of a fossil fuel or a nuclear reactor.
A steam turbine comprises (1) a rotor, or series of rotors on a shaft, with blades attached to the rotor(s), (2) a casing for the rotor that serves as a pressure vessel for containing the steam and accommodates fixed nozzles through which the steam is accelerated before being directed against the blades attached to the rotor, (3) a mechanism to regulate the speed of the rotor, and (4) a support system for the bearings that support the rotor. The rotor of the steam turbine turns as steam impinges against blades attached to the rotor. When the rotor is turned, it turns the electromagnet of an electric generator, which produces electricity.
In a typical steam turbine system, water is converted to steam by a steam generator and transported to one or a plurality of turbines, e.g. a high pressure a (HP) turbine, an intermediate pressure (IP) turbine, and a low pressure (LP) turbine, all coupled to a common shaft to drive an electrical generator. Steam generated from the steam generator is directed through the HP, IP, and LP turbines through a main steam line via main steam valves and a control valves. As the steam passes through one or the plurality of turbines, pressure and temperature changes occur. At or near the exit of the low-pressure turbine, the steam undergoes an expansion and is moisturized. The moisturized steam exiting from the low-pressure turbine transported to a condenser, where it is condensed and eventually returned to the boiler of the steam generator.
If high-pressure, high-temperature steam is partially expanded through a turbine, the efficiency can be increased by returning the steam to the steam generator and re-heating it to approximately its original temperature before feeding it back to the turbine. Single reheat turbines are commonly used in the electric utility industry. For very large units, double re-heating may be employed. Non-reheating turbines are currently limited mostly to industrial plants and small utilities.
As was mentioned previously, a steam turbine often is connected to a condenser. A condensing steam turbine condenses the steam below atmospheric pressure to gain the maximum amount of energy from the steam. In non-condensing turbines, steam leaves the turbine above atmospheric pressure and is then used for heating or for other processes before returning as water to the boiler.
The efficiency of a steam turbine is typically measured by its xe2x80x9cheat ratexe2x80x9d, which is the amount of heat that has to be supplied to the feedwater in order to produce a specified generator power output. The heat rate is the heat input in BTUs per hour for each kilowatt-hour of electricity produced. Among other factors, the heat rate depends upon the amount of copper deposit built up on the turbine blades of the steam turbine. The lower the heat rate, the less the thermal energy required and the better the efficiency.
Turbine efficiency is calculated by comparing the actual versus theoretical steam flow rates, the actual versus theoretical steam temperatures, and the actual versus theoretical electric energy produced.
The oximes used in this process are described in U.S. Pat. No. 4,487,745 which is hereby incorporated by reference and shown by the following chemical structure: 
wherein R1 and R2 are the same or different and are selected from hydrogen, lower alkyl groups of 1-8 carbon atoms and aryl groups, and mixtures thereof, particularly aliphatic oximes. Most preferably used, as the oxime, is methyl ethyl ketoxime (MEKO).
The oxime is fed into the electric generating power plant at any injection point where the oxime is activated and the steam will come into contact with the turbine blades. In order to activate the oxime, the oxime is added to an injection point that exposes the said methyl ethyl ketoxime to a temperature of about 30xc2x0 C. to about 320xc2x0 C. The oxime is injected at a point in the system, so that the oxime will eventually contact the blades of the rotor of the steam turbine.
Examples of such injection points for the oxime include the pre-boiler system of the steam generator, the boiler steam drum of the steam generator, the feedwater of the lower pressure steam turbine, the highest-temperature feedwater heater extraction steam of the lower pressure steam turbine, the main steam header prior to the turbine, and the turbine crossover piping.
Preferably the oxime is fed into the highest-temperature feedwater heater extraction steam of the lower pressure steam turbine and/or the boiler steam drum of the steam generator. This will not only improve operating efficiency, but also maintains cleanliness, while minimizing the potential for damage to the system components. The addition of MEKO to these injection points, in an amount sufficient to obtain a residual of at least 5 ppb in the steam exiting the steam drum, will result in increased operating efficiency of the steam turbine. Although it is preferable to add the oxime to an injection point already existing in the electric generating power plant, it is possible to create special valves or openings that serve as an injection point for the oxime.
The typical dosage of oxime used to reduce copper deposits on steam turbine blades is at least 1 ppb, preferably at least 5 ppb, and most preferably, at least 50 ppb. However, the oxime dosage, in most cases, is not expected to exceed 250 ppb. Preferably, the oxime is fed continuously, and the dosage is typically maintained for a minimum of 1 week, preferably from 2 to 4 weeks. Typically, the feed time for the oxime does exceed 12 weeks. The oxime is typically injected at a pressure of approximately 50 to 3500 psig at the injection point.
The operating efficiency of the high-pressure turbine, intermediate-pressure turbine, and low-pressure turbine increases by the addition of the oxime.